The ballistic missile submarine USS Montana sinks under mysterious circumstances. US Navy SEALS are brought in to salvage the sub.s missiles and an experimental civilian deep water oil-drilling rig is commandeered to help. During the operation, freak weather conditions damage the platform and sever its communication with the surface. As World War III looms above and tensions rise between the divers and a deployed SEAL team, the rescuers discover that there is something else besides the submarine in the Abyss.